There were 17 suspected cases of the virus as of last Friday at Houghton Elementary School, Graden said.

Now, there are sporadic suspected cases being reported at other elementary schools and the middle school, said Graden, who did not have an estimated number of new cases Wednesday. He said school officials believe the new cases are being reported in siblings of the students who were ill last week

"We had notified parents at Houghton. Now, we are making more families aware that there are more (cases) now," Graden said.

There are no reports of the virus in other area school districts, according to Laura Bauman, epidemiologist at the Washtenaw County Health Department.

Onset: Symptoms usually begin about 24-48 hours after exposure, but they may appear within 12 hours. The illness begins very suddenly and the infected person feels very sick.

Treatment: There is no treatment for the virus itself. Drink fluids to prevent dehydration. Contact your medical care giver if you are concerned about dehydration or other unusual symptoms.

Prevention strategies: Wash your hands often, using soap, warm water and friction. Clean and disinfect all contaminated surfaces with a solution of 1 part bleach to 10 parts water. People with symptoms should not prepare food for three days after they have recovered.

Noroviruses are a group of viruses that cause acute gastroenteritis in humans, according to information from the health department. Symptoms of norovirus infection include nausea, vomiting, diarrhea, cramping, and low-grade fever.
Symptoms usually begin about 24-48 hours after a person has been exposed. The symptoms can last one to two days.

Among the ways the virus spreads is through the consumption of food or water that has been contaminated with the virus or through direct person-to-person contact. Handwashing, especially after using the restroom, is important in preventing spread of the disease.

The county's public health nurses have been consulting with the district's nurse about the illnesses, Bauman said.

School officials have also been notified about the importance of disinfecting classrooms and offices.

Graden said doorknobs, faucets, sinks, toilets, tables and other areas in the classrooms and offices are being disinfected with the bleach solution.

"The most important thing is using a bleached-based cleaner that can kill this bug," Bauman said.